HEUI system components (1)

atmospheric pressure sensor

The atmospheric pressure sensor (1) is installed on the hydraulic supply pump group adapter and is vented to the atmosphere. A foam block below the sensor helps prevent the entry of dirt into the sensor. The sensor performs the following functions:

  • Ambient pressure measurement for automatic altitude compensation and automatic air filter compensation.
  • Absolute pressure measurement for the fuel ratio control, ET, Caterpillar Monitoring System panel (gauge) pressure calculations.

The fuel temperature sensor (2) is used for automatic fuel temperature compensation.

hydraulic pressure sensor

The hydraulic (injection actuation) pressure sensor (arrow) is located between the valve cover bases in the right fluid supply manifold.

The hydraulic pressure sensor is used to measure injector actuation hydraulic pressure for the ECM.

The ECM uses this pressure measurement to control the displacement of the hydraulic supply pump (through the pump control valve).

timing callibration

The timing calibration sensor (arrow) is installed in the flywheel housing.

This sensor (magnetic pickup) is installed in the hole normally reserved for the timing pin. (The pin is used to position the crankshaft with the No. 1 piston at top dead center.)

The timing calibration sensor is permanently mounted on the D9R because of accessibility.

turbo inlet pressure

The turbo inlet pressure sensor (arrow) is mounted between the air filter and the turbocharger.

This sensor is used in conjunction with the atmospheric pressure sensor to measure air filter restriction for engine protection purposes. The difference between the two pressure measurements is used as the filter differential pressure.

The engine ECM uses this calculation to determine whether derating is necessary to protect the engine.

turbo outlet pressure

At the front of the engine in the right cylinder head is the turbo outlet (boost) pressure sensor (arrow). This sensor is used with the ECM to control the air/fuel ratio electronically. This feature allows very precise smoke control, which was not possible with mechanically governed engines.

The sensor also allows boost pressure to be read using the service tools.

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